Shielded loop



Sept. 13, 1932. L. o. MARSTELLER SHIELDED LOOP Filed Feb. 4, 1928 2Sheets-Sheet l INVENTOR Zes ATTORNEY Patented Sept. 13, 1932 LESTER o.MARSTELLER, or IRWIN, PENNSYLVANIA, AssIeNon ro WESTINGHOUSE I ELECTRIC& MANUFACTURING COMPANY, A. CORPORATION OF PENNSYLVANIA SHIELDED LoonApplication filed February 4, 1928. Serial No. 251,851. I

This invention relates to radio reception,

, and more particularly to receiving devices which are intended todetermine the direction from which the received signal comes.

. A loopantenna is more receptive to signals t io directions at rightangles to the plane of the loop. :The theoretical diagram representingthe response to signals from diiierent directions is a figure 8 made oftwo circles tangent to each other. The maximum change of rer sponse.with changeof direction is at the point where the two circles aretangent. This is the reason why it is the practice to obtainthedirection by setting the loop to the positionfwh-ich gives minimumresponse.

.5120 Although the response may become a min imum, it willnot, with theloops heretofore used, ordinarily becomelzero, because, super posed uponthe directional effect of the loop, represented by the figure 8 diagram,there r is a non-directional efiect usually known as the antennaefiectf" The 1 theoretical diagram corresponding to this efiect is acircle, "and the super-position of the circle upon the figure 8 diagramleaves no zero point but only two places of minimum. response. i it Thisso-called antenna efi'ect is largely the result of the action of thevertical wires from the loop -tothe receiving set. If these wires werecompletely shielded from the signal, the antenna effect would be verysubstantialdiminished. Frequently, an antenna efl'ect 11spurposelyintroduced, either by an extra loop or by a non-directionalantenna.

" efiect with the. loop eifect it is possible to of the shield will havea constant directional certain amount of antenna effect is degsirablebecause it may be combined with the determine the sense of the travel ofthe signal, that is, inthe,illustration chosen, whether the signal comesfrom the northeastor from the south-west;

For the purpose ofobtaining an indication'of the sense, it is necessaryto reverse the antenna efi'ect relative to the loop efiect. This cannotbe done when the antenna eiiect .and the loop effect are both obtainedfrom one system of receiving wires.

'60 Signals which arrivein directions in the plane of the loop producethe maximum efiect therein. a If all signals, except these, can beprevented from producing any result in the loop, a greater certainty inthe determination of the line of the direction from which the signalarrives will result.

It is an object of my invention to provide means for shielding the loopfrom signals which arrive from any direction except those 7c. in theplane of the loop.

Itis a;further object of my invention to provide shielding means whichhave a directional characteristic.

It is a furtherobject of my invention to mechanically associate theshielding means and the-loop, whereby they will rotate together, and thedirectional efi'ects of loop and relation. s0

It is a furtherobject of my inventionto provide ashield of minimumWeight, maximum effectiveness and great directive effect.

It is a further object of my invention to so position the shieldrelative to the, winding of the loop that the capacity effect betweenthem shall produce no objectionable diminution of the tuning range. i

It isa further object of my invention to so select the position of theshield relative to the winding that the capacity effect between themshall not render'the set unstable.

It is a further object of my invention to provide an antenna, distinctfrom the loop, and to so separate the antenna'lead-infrom the looplead-in that the antenna efi'ect in the loop and its lead-in shall notbe increased by the effect of the antenna lead-in.

It is a further object of my invention to provide a convenient switchingand .adjustand partly in perspective, of an apparatus constructedaccording to my invention, and;

ing means whereby, when the loop is being used to determine the line ofthe direction, the system shall have maximum sensitiveness and whenthe'loop and antenna are being used together for determination of thesense of said direction, the combination of the, two shall be mosteffective. 7 1

Other objects of my invention and details of the construction willbeapparent from the following description and the accompanying drawings,in which Flgure 1 is a view, partly diagrammatic Fig. 2 is a diagram ofthe circuits and apparatus. r 7 1 A loop 1 is providedwhich-constitutesa directional antenna. The loop includes a winding 2 supported within a micarta housing "comprising an inner channel member 3and "an outer channel member 4: telescoping therewith. The channelmembersare secured together by means of micarta angle bars 5 riveted toeach member. The winding is supported by means of micarta brackets, 6,one at each corner of theloop, mounted at the junction of each pair ofadjacent lengths of nelmembers between said angle members and.

the 'innerehannel member 3. Preferably, the br-ackets 6 are provided attheir outer edges with notches to definitely position the indiv-idualturns of the Winding.

V The housing, composed of the micarta' channel members, is supported bydiagonal members 7 which are provided, at each'end,

with blocks "8 to set into thecorners of the loop housing and to whichthe-housing'may be s'ecuredin any desired way. The several lengths ofhousing are fastened together, at the corners of the loop, by meansofjmet-alcaps 9 provided with lugs. I Bolts, extending through the lugsand through angle members 11 on the inside of the loop, secure thechanflanges on the outside edges of the caps.

' Within the housing, held in place between the inner channel 8 and theouter channel 4, lengthslQ of .copper are provided. At each corner ofthe loop, except one, these lengths 0 aresoldered together. They thusform two polygonal strips each of which has the form of the outline ofthe loop. There is one strip on each face of the loop and eachstripcomprises as many lengths as the loop has sides. The lengths stand withtheir widths at right angles tothe plane of'the wires of therespectiveisides-of the loop and extend past such plane in bothdirections, that is, the winding is approximately mid-Way betWeentheouter 'andthe inner edges of the metal strips.

At one corner of the loop,-the outline fforrne'd' by a copper strip 'isinterrupted by a gap, as shown at 13. The gap in the other Isitrip maybe at the same or at a different corner. The'loop, housing, frame andstrips are all mechanically united together and mounted in any desiredway to rotate, as indicated by the bearing 14.

Preferably, the rotational mounting includes a hollow metallic mast orvertical" pipe 15 through which the leadin wires from the loop extend toa plug at the back of the receiving set 16. The mast or pipe 15 ispreferably long enough to enable the wires to move with the rotation oftheloop with out becoming twisted enough to cause likelihood of theirbreaking. .On the other hand, the wires are made as short as possibleand provide for, this motion. Excessive twisting may be avoided byproviding a stop to prevent, rotation of loop through several though, ifdesired, the lead-in wires may all enter the case through one plug.

:The wires inside the pipe ,15'include a lead '25,best shown in Fig. 2,from one end of-t'he winding of the loop, a lead 26 from the other endof the windinganda lead ZT from the mid-point of said winding. 7 Thecopper strips12 are'connected in any suitable way, '1 I 00 for example,by solderedlugs, to each other and I to the leadin wire 27. ,Between:the

lead-in wires-25 and'f26 an' adjustable condenser 28 is connected, whichis manipulated by means ofthe drum, receiving set lfi.

The wires '25 d 27 are connected, respectively, to tlie grid andthefilament of a vacuum-tube amplifier 30. The plate of said amplifieris connected through the primary 31 of a transformer, to the usualBbat-tery 32. The plate is also connected, through a neutralizingcondenser-33,- to the wire 26.

The secondary 34,01 the transformer is connected to th rid and filamentof a 131011 includes a resistor 36. The'secondary is tunedby means ofan, adjustable condenser.

3'1 which is manipulated by the same drum ,29 on the outside of t-hereceiving set. {The rotors of the two-condensers 28 and 37 aremechanically connected to each other in order that they may be operatedby the one control drum; 1 I

I The antenna 20 is connected to one ter- 'minal of a switch 40. Whenthis switch is'in :circuit closing position for this ter- 9 on the frontof the r r v sec- 0nd vacuum-tube amplifier 35.. The connecniinal, theantenna is connected thereth'rough toan adjustable contact all on theresistor 36. The. antenna is'thereby connected to an cuit of theamplifier 35. i The output circuit of fconn'ectedto the next tube of areceiving set.

1 intermediate point; of the grid-filament cirthe amplifier s5 is Thereceiving set includes the tubes and i and whatever additionaltubes arenecessary." Amongthe additional tubes will beat leastone detector."The'arrangement ofthe tubes constitutes no feature of my invention and,consequently, it is shown only diagrammatically by; the rectangle 4:2.

j In the preferredform of my device, the

additional tubes, indicated by the rectangle "1 42, also include anoscillator tube for hetero- '5 dyningl The' frequency generated bytheoscillatingtube is controlled by an adjustable cond'ensermanipulatedfrom the outside of.

thesetby means of the drum 38. The signalsfrom thereceiving set areheard in the telephones 43. The filamentsr of the tubes .30 and 35-andof other tubes in the receiving setareenergized from the A battery. 44 iand the plate circuits of thereceiving set i The resistance thereof isthusremoved from are supplied fromthe B battery 32.

1; Whe1i the switch is in the right-hand position, a connectionvisestablished thereby from one end ofythe resistor '36 to the other.

thewinputcircuitof the amplifier 35.

In the operation of the device, radio waves carrying signals lmpingeupon the loop 1. If these-waves are exactly in the plane ofthe loop theymeet the sheet-metalstrips 12 edgewise; Consider the loop in a'vertical,northand-south plane and a signal from a station situated to the northof the loop. The electrostatic-component ofthe signal wave is thenvertical. 'Itgives rise to a current inthe same direction in both sidesof the loop and thus tends to produce no resultant electromotive forcearound the loop. The width of the loop is so small, compared to thewave-length ofthe signal, that the difference of the effects in the two;sides of the loop may be neglected.

{The electromagnetic component of the. Sig-1 nal wave, on the otherhand, is, under the" 1 circumstances stated, in a horizontal east?and-west direction. It; therefore, produces a 5 change of flux throughthe loop andso gives W 0 rise to an electromotive force around the.loop. It also gives rise to an electromotive forcearound each of thetwocopper frames [constituting theshield. The'electromotive force aroundthe loop gives rise to a current through the condenser 28but;1because ofthe opening 13 in each frame, no currentar'ound the frame results.

The capacity betweenadjacent edges of the copper .stripat 13istoosma1lto pass any j to;

i stripsfone' on each face of the loop, a copper 1 pipe enclosing thewinding extended around i the loopexceptfora single circular crack atthe ends of the pipe, the capacity across the crack would be much largerthan that across substantial current. If, instead ofithe two readilyobserved as possible. Consequently, the shield comprising thetheopenings 13. Such a pipe would, therefore, cause a. much greaterdiminution of the signal than the strips cause.

The electromagnetic component of the signal wave, under the assumedcircumstances, is a changing magnetic field atiright angles to the planeof the copper strips. It, therefore, gives rise to eddy currents in thestrips which do not require for their circulation that eachof the copperframes shall form a closed circuit. Some of the energy of the signalwave which would otherwise be expended in producing current in the loopis, therefore, absorbed in the copper shields.

If, with the signal in the same direction as before, the loop be turnedabout a vertical avoided when the loop is to be placed in po V sition ofzero response, because it is then necessary that any elfect whichresults from a slight difference, between the actual position and theposition of 'zero response shall'be' as two copper frames 12 assists inobtaining more accurate settings for zero response.

The signal waves cause currents in the Winding 2 and, consequently,voltages are impressed upon the grid-filament circuit of the tube 30.The condenser-28' cooperates with the inductance'of the winding 2 toform a 3 resonant circuit for the frequency of the signal waves, .andthereception through the tube 30 is thus rendered sensitive. v

The capacity between a strip 12 and the neighboring turns of the winding2, in series with the capacity between the other strip 12 and the turnsof the winding 2 nearest it, constitutes a capacity in parallel with thecondenser 28. This somewhat increases the minimum capacity to which theadjustment" 'Tlie range may be made by the drum 29. over'whioh theloopmay be tuned is diminished by this increase of the minimum capacity. Thedistancebetween the copper strips 12 and the wire 2 must be so chosenthat this each range of wave length, a compromise position mustbeadopted.

When thesignal waves arrive from any other directionthan that of theplaneof the loop, the strips 12 act as a shield. Theenk ergy of thewaves is'absorbed as eddy currents in thesheet metal anddoes not reachwill be elipses tangent to each other at the ends of the minor axes. Ifsuch diagram be compared with the. two circles, it is easy to understandthat a very! small change inzthe angle between the loop and the signalpro-f ducesa larger departure from the, minimum signal in the case ofthe shielded loop than inthe case of the ordinary loop.

. the outside of the receivingset.

, Signals which impinge upon the antennaQO produce substantially thesame effect from whatever direction they arrive. If the switch 40 is inthe left-hand position, these signals are impressed upon the inputcircuit of the tube 35. The extent to which they affect this circuit iscontrolled by adjustingthe position of the contact member 41'.

' This may be controlledby the knob 44L on If the adjustment be properlychosen, the energy in the circuit 34:-37 from the antenna 20 and theenergy therein from the tube 30,

" which is controlled by the loop 1, will be opposition can beaccomplished equal. Then, if the phase of these two currents isopposite, the sound in the telephone 43 will be a minimum. 011 the otherhand,

if these two are in phase with each other,ja maximum signal willbeheardin thetelephones.

Thechange in phase from coincidence to by rotating the loop 1 through180.

a In using the apparatus,the operator will first place the switch 40 tothe right in Fig. 2,

which corresponds to'the upper position in Fig. 1. He willthen'rotatethe loop 1' until he obtains a minimum signal. During thisoperation, the resistance of the rheostat 36 isshunted out of the gridcircuit of the tube 85. The amplification is, therefore, most effectiveand best suited for determining the position of the loop 1 which willgive minimum signal. 1

'Having found in this way the line ofthe direction of the arr'vingsignals, the operator moves the switch 40 to the left." "He then rotatesthe loop through to bring it into a position ofi'naximum' signaLf Henotes the signal intensity'and then rotates the loop through and noticeswhether there-is any difference in intensity of the signals in the twopositions. He next'moves the handle 44:,

1,877, see

which adjusts-the contact 41, andagain re verses the loop. A few trialswill enable him to find a position for, the contact :41 in which the.difierence in the signal strength which occurs upon rotating the loop180 is readily observed. 'f i He is then able tolearn the sense ofdirection of 'the signal because that edge of 1 theloop 1 which willyield a signal in phase with the signal in the antenna 21, when directed toward the arriving signal, is made. to

correspond to an identifying mark upon the pointer mechanicallyconnected withjthe loop. The direction of themarked end of the pointer,-when the maximum signal is received, with the switch 40 in the left-handposition, indicates the direction'from which the signal arrives. f y

' It will thus be clear that the apparatus affords a means for moreaccurately obtaining the line of direction of the signal and then,-

quickly and conveniently obtaining the sense of the direction. 7 r

Although I have described the insulating parts of theloop supportandloop housing as'being of micarta, otherinsulatingmaterial in whichthe high-frequency losses are not too great, may be used. I havedescribed the shield 12 as of copper; it will, however.

be evidentthat'any conductor will serve for ashield. It is quitepossible to use, instead of a separate piece of metal, a plating ofcopper orother metal:electrolytically disposed upon the micarta housing.Moreover, many of. the parts hereindescribed as of insulation may bemade of metal, althoughinsulation is preferred in the parts thusdescribed. The

angle bars 5 are an illustration of this. These bars maybe made of metalinstead of insulation although better. results are obtained ifinsulationis used.

Although I have specifically described and illustrated only a singleform of my inven- *tion, it will be clear [10 uno'se-skilled in'the'artthat many modifications may be .made without departing from the spiritthereof. )1, therefore, do not intend to'be limited except as'requiredby the prior artand indicated in the claims.

I claim as my invention: 1. In a radio compass, a directive antenna, anon-directive antenna, an amplifier having its input connectedto saiddirective. antenna, a second amplifier, means for combining the energydelivered from the output of said 7 first-named amplifier with energyreceived from saidnon-directive antenna and impressing the combinedenergy upon said second amplifier, and means associated with said'secg1? f :1

0nd amplifier for adjusting the amount of energy received from saidI101'1-d1I6Ct1VQ2tIltenna. 7

In aradio compass, a directive antenna, 7 V

a non-directiveantenna, an'amplifier having j its input connected tosaiddirective antenna,

a second amplifier, means for combining the energy delivered from theoutput of said firstnamed amplifier with energy received from saidnon-directive antenna and impressing" the combined energy upon saidsecond amplifier, means for adjusting the amount of uenergy receivedfrom said non-directive antenna, and switching means for, at will, pre-H venting the delivery of energy from said non- .directive antenna tosaid combining means. i 3. In a radlo recelvlng system, a non-d1- grectiveantenna, a vacuum-tube amplifier, a resistor 1n the mput'ClI'Cllli) thereof, a directime antenna. connectedto said inputcircuit,

and a switch, in one position, connecting said non-directive antenna toan adjustable point of said resistor and, in another position,establishing a shunt about said resistor.

4. In a radio compass, a loop antenna havingsubstantially parallelfaces, a shield on each face of said loop parallel thereto, each shieldcomprising an open strip having a contour like that of the loop, saidloop being unshielded between said shields.

5. In a radio compass a loop mounted for rotation about a vertical axisand shielding means mounted to rotate with said loop, said shieldingmeans including spaced parallel portions so positioned relative to theloop that they tend to exclude signals, from all directions exceptthoseto which the loop is most receptive.

6. In a radio compass, aloop comprising a winding and a tuning device,spaced shields,

winding and a tuning device, a shield on each face of said loop andcomprising a metal member, said members constituting a laminatedstructure.

In testimony whereof, I have hereunto subscribed my name this first dayof February,

i LESTER O. MARSTELLER.

one on each face of said loop comprising a metal member positioned asclose to the winding of the loop as possible without materiallydecreasing the tuning range.

7. In aradiocompass, a loop comprising a r winding having a plurality ofturns, a shield on each face of the loop, each shield comprising asheetof metal constituting a strip in a a plane perpendicular to thesurface of the winding and forming an outline having the contour of theloop and open at least one point. I

8. In a radio compass,,a Winding comprising a plurality of turns,supporting means for positioning said turns, shielding means linecorresponding to the contour of the loop andextending across saidsurface.

10. In a radio compass, a loop comprising a

